Catch devices have been provided heretofore to protect roll-up doors, roll-up grates, roll-up grills and roll-up gates forming closures for protected areas, against undesired unrolling. Such devices have generally comprised a brake wheel which can be fixed to the windup shaft and which is provided with a brake body on the brake wheel engageable with a stationary housing.
Such catch devices prevent the uncontrolled unrolling of the door, grate, grill and gate by braking such movement. The shaft can have a worm wheel provided for this purpose.
In one prior system as described, for example, in German patent document DE-GM 82 25 405, the brake element is constituted as a ball detent which is dependent upon centrifugal force for its functioning and can be structurally independent of the worm drive.
In practice, the worm drive or transmission which winds up the door or the like is provided at one end of the shaft while the catch device is provided at the other end of this shaft. The arrangement of the catch device as a ball detent system independently of the worm transmission and as a separate unit is comparatively expensive.
Basically this drawback also characterizes the safety device for roll-up doors described in German Pat. No. 24 41 522.
In this case, the brake wheel is provided with spaces in which balls are arranged and upon an excessive acceleration of the wind-up shaft, the balls are pressed against the edge of the transmission housing.
The housing is provided with an appropriate recess for this purpose into which a ball is pressed so that the ball is clamped, based upon the dimensions of the recess and the ball into a gap which becomes progressively smaller between the housing and the wheel to block rotation of the shaft.
Apart from the fact that this latter catch device is relatively expensive and the machining of the parts for it must be carried out with low tolerances to ensure that the ball will jam properly in the gap, it is a disadvantage that the braking action takes place with point contact between the ball and the structures engaged thereby. To prevent destruction of the ball and thus a loss of braking effect with time, the pawl must be composed of a correspondingly hard and wear-resistant material.